Method of preparing resistance units



Dec. 9, 1930.

| o. GRONDAHL 1,784,435

METHOD OF PREPARING RESISTANCE UNITS Filed Nov. 7, 1 2

. INVENTOR 2 76a. W44 BY Q'Z-M N14 ATTORNEY Patented Dec. 9, I

" UNITED T TES PATE T OFFICE LARs o. GRONDA-HL, or PITTSBIJ'RGH,- PENNSYLVANIA, ASSIGNOR 'ro THE UNION swI'rcII & SIGNAL com'rANy, or SWISSVALE, PENNSYLVANIA, A CORPORATION or iENNSYLVANIA Application filed November My invention relates to resistance units and to methods of preparing the same. I will describe one form of resistance unit, and one method of preparing such unit, and 5 'will then point outthe novel features thereof inclaims. I I I In the accompanying drawing, Fig. I is a top planvi'ew showing a blank suitable for I preparing one form of resistance unit accord- 10 ing to my invention. Fig. 2 is a sectional View along the line II II of'Figpl. Fig. 3 is a view similar-to Fig. 2, showing the resistance- O i a I 0 tage; of this characteristic in electrical circuits, however, it is necessary to prepare re Si-stance units of these substances,;wh'ich units may be inserted in electrical circuits in any desired manner. Due to the mechanical 0 characteristics of these substances it has been diflicult-or impossible, with the processes hitherto available, to prepare such-units with a sufficient degree of'mech'anical strength and; i

- electrical I uniformity to be commercially 5 practical. I Y

In resistance units prepared in accordance with my invention howe \-'e1-','these disadvantages have been completely overcome. 7

Referring now to Figs. 1, and 2, therefer ence character A designates a flat blank of the metal which forms-the base of the thermo sensitive substance. For example the blank may be of copper or'iron; As best shownin Fig. 2,this blank isformed wit-h comparativelyvthin bridge portion 3 intermediatethe ends of the blank. Each of theend portions'2 A may be provided with a hole 1, the purpose of which will appear hereinafter.

tively thick end portions 2, and a compara- The blank A is first treated chemically to METHOD OF PREPAImwG RESISTANCE UNITS 7, 1925. semi No. 67,552.

formthe thermo-sensitive substance directly on the metal. F or example "when-the blank is copper, it'may be heated in "the. presence of air to form copper-oxide. This chemical treame'nt is continued until the bridge portion 30f the blank .is' changed entirely to the I a portion of theirsurfaces, leaving the plates "connected-with the bridge-3 as shown in Fig.

:4. The oxide may be removed by any suitable means such as a sandblastor nitric acid.

:-The base plates 2 provide convenient terminalsto which binding posts may be attached for'connecting the unit with an outside elec:

'trical circuit. These binding-posts maybe inserted-in the holes 1 in the plates 2.

Since the thermmsensiti-ve --niaterial is formed directly'in contact with the terminal plates :1 perfect, electrical contact is assured, and-copper oxide, prepared in the manner I have described, has sufficient mechanical strength to withstand severe jars, vibration and rough handling.

i Although I have herein shown and described only one form. of resistanceu-nit em;

bodying my invention 'and only one process I of preparing the same, it is understood that various changes and .niodifications may hemade/therein within the'scope of the appended claims without departing from the spirit and scope. of my invention.

Having thus described my invention what lclaimisf 1. The method of preparing-a resistance unit from a blank of metal having a comparatively thin bridge portion and two comparatively thick end portions which consists" in chemically treating said blank to form a compound of the metal until said bridge portion is changed-entirely tolthe compound but a entirely stopping the chemical treatment before the end portions are entirely changed to such compound, and removing a portion of the compound from the end portions.

2. The process of preparing a resistance unit which consists in forming a substantially flat metallic blank with a bridge portion of reduced thickness, chemically treating the blank to change said bridge portion to a compound of the metal but stopping the chemical treatment before the other portions are entirely changed to such com- 7 pound, and removing the compound from the said other portions of the blank.

3. The process of preparing a resistance unit which consists in forming a substantially flat metallic blank with a bridge portion of reduced thickness, oxidizing the blank to change said bridge portion entirely to oxide of the metal but stopping the oxidation before the other portions are entirely changed to oxide, and removing the oxide from the said other portions of the metal.

4. The process of preparing a resistance unit which consists in forming a substantially fiat copper blank with a bridge portion I of reduced thickness, oxidizing the blank to entirely change said bridge port on to copper oxide but stopping the oxidation before the other portions are entirely changed to such oxide, and removing the oxide from the said other portions of the blank.

5. The process of preparing a thermo-sensitive resistance unit which consists in'forming a substantially flat copper blank with a bridge portion of reduced thickness intermediate its ends, heating the blank in the presence of air to change said bridge portion-ent rely to copper oxide but stopping the heat treatment before the end portions are entirely changed to copper oxides, and removing the oxide from the end portions of said blank.

In testimony whereof I afiix my signature.

LARS O. GRONDAHL. 

